It is a continuing goal in the metal cutting industry to provide metal cutting inserts with sharp cutting edges that stay sharp longer even when machining non-ferrous and abrasive materials. To this end, it has been known to incorporate polycrystalline diamond (PCD) materials and polycrystalline cubic boron nitride (CBN) materials on a carbide substrate to provide an improved cutting edge. However, a significant portion of the cutting tip is embedded within the slot and this embedded portion acts only as structural material to retain the tip within the slot and does not contact the workpiece.
The cost of PCD or CBN materials used as a substrate is very high as compared to the cost of cemented carbide. One attempt to reduce cost is to provide a cutting insert that incorporates a discrete cutting tip that wraps around the nose of a cutting insert and having a top layer made of PCD or CBN material that is supported by a bottom layer of cemented carbide substrate. It has been found, however, that although the top layer of PCD or CBN material has sufficient thickness for allowing a chip breaker to be ground therein, the thickness of the top layer of PCD or CBN material is insufficient for machining operations, thereby reducing the machine life of the cutting insert.